How is this ban actually enforced? By fining American companies for serving specific content. That is the First Amendment issue. SCOTUS simply asserting that it's not in order to make their ruling convenient does not actually make it so.
Is that also free speech? Again, it's just the law and how it is enforced.
"Foreign governments saying things" also existed at the same time the 1st Amendment was written, and there were no carveouts from 1st Amendment in light of that.
In any case: If SCOTUS during its early cases on copyright law (or copyright on the Internet) simply asserted "this has nothing to do with the 1st Amendment," they'd also be wrong. That would be a clear avoidance tactic not to wrangle with the substantive issue. In reality, the big cases on copyright are riddled with 1st Amendment questions, considerations, and constraints.
No, it fines American companies for providing services to a certain foreign-owned company.
If this isn't permissible, then sanctions can't be a thing and OFAC can't do its job. (Whether or not that would be a good thing is a separate issue.)
A SCOTUS that simply asserted these questions do not exist would also be laughable.
One very recent entry on this discourse:
https://knightcolumbia.org/content/knight-institute-and-foun...
The law indeed needed to be carefully written to "skirt" any first amendment violations, and SCOTUS unanimously agreed it had done so successfully.
Universal City Studios v Corley